Abstract:To discuss the feasibility of using the fly ash and industrial slag solidified dredged sluge as roadbed material, a series of laboratory tests were performed to investigate the effect of curing agent ratios on the compaction properties, water stability, bearing capacity and shear strength. The test results showed that the maximum dry density of the solidified sludge with different curing agent ratios are higher than 1.50 g/cm³, and the optimum moisture content are about 20%~21%. The soaking induced expansion rate with the soaking time of 4 days are less than 1.1%, which indicates the water stability are ameliorated after solidification. With the decrease of fly ash and the increase of mineral powder, the CBR(California bearing ratio) and the shear strength are greatly increased. The solidified sludge with different curing agent ratios have high CBR after soaking for 4 days. The sample of SD10FA20MP has the highest CBR (34.8), which is 4.35 times of lowest requirement of roadbed filling of highway. It is concluded that it is feasible to use the fly ash and industrial slag solidified dredged sludge as roadbed filling material.

Abstract:Pull-out tests were carried out on 72 concrete specimens reinforced with 600 MPa high strength reinforcement to investigate the bond-anchorage properties between 600 MPa high strength reinforcement and concrete. Failure pattern and bond stress distribution of specimens were studied, respectively. The bond-slip constitutive relations of 600 MPa high strength reinforcement were established through basic form of bond-slip and position function. Through establishing the calculation formula of ultimate bonding strength for 600 MPa high strength reinforcement, bond-anchorage length was established via reliability analysis of JC. The results showed that the failure pattern, bond stress distribution between 600 MPa high strength reinforcement and other strength reinforced bars no obvious difference. Basic anchorage length formula of GB50010-2010 still can be applied to 600 MPa high strength reinforcement.

Abstract:The rheological properties of river sludge mixed with cement and air foam were studied by shear rheological test. The test results showed that under the load the mixed lightweight soil by curing process was similar to the rheological characteristics of hard clay. The soil rheological curve of air foamed soil using river sludge mainly presented three models. When the shear stress level was low, the theological curve appears as attenuation stable; When the shear stress levels continued to increase, the form of the rheological curve was not stable but constant speed type; When the shear stress increased to a certain extent, the rheological curve type was accelerated. With the improvement of the strength of the mixed lightweight soil, the rheological properties of river sludge mixed with cement and air foam is reduced. According to the test, the mixed lightweight soil shear rheological conformed to the seven-component visco-elastoplastic shear rheological model. Using the model can reasonably and reliably describe the rheological process include attenuation, velocity and acceleration of the mixed lightweight soil under various shear stress levels.

Abstract:Process of chloride ion diffusion in concrete with cracks is studied to accurately assess durability performance of concrete structure with cracks. Preparation of cracks with nondestructive method is proposed, which can produce cracks in internal concrete or on its side face effectively. Chlorine salt solution immersion experiments on the concrete with cracks is conducted. It is studied on the chloride ion diffusion effect of specimen with single slit and double slits, and revised chloride ion diffusion coefficient, and simulating chloride ion diffusion process of concrete with cracks. Research results show that the chloride ion diffusion will occur along or perpendicular to the cracking direction, and decreasing of the water cement ratio, resistivity to chloride ion diffusion in cement mortar specimens increased significantly. In a specific range, increasing cracks spacing, the chloride ion diffusion interaction between double slits obviously decreases. And simulation results in ANSYS are in good agreement with those data obtained in test.

Abstract:The sectional form of steel-concrete-FRP-concrete (SCFC) column, as a novel composite column, has a steel tube as the outer layer and a circular FRP tube as the inner layer, and concrete filled between these two layers and within the FRP tube. Considering the confinements from both outer steel and inner FRP layers, the twin shear unified strength theory and force equilibrium condition are utilized to develop an analytical model of bearing capacity of SCFC column. The accuracy of the proposed model is evidenced through being compared with experimental data. The parametrical study is conducted in order to evaluate the confinements affected by the sectional steel proportion, ratio of FRP to steel, ratio of diameter to thickness of FRP and FRP diameter itself. The results indicate that the greater sectional steel proportion, the larger ratio of FRP to steel, and smaller ratio of diameter to thickness of FRP have positive contributions on the confinements of SCFC. The ratio of FRP diameter to steel side length locates between 0.65-0.75 can lead to a better confinement.

Abstract:Carbonation of recycled coarse aggregate (RCA) concrete was a complicated physical diffusion and chemical reaction process, which was difficult to analyze and predict. According to the carbonation mechanism of the RAC concrete, a multi-field coupled model for carbonation analysis of the RCA concrete was developed by combining the diffusion rule of CO₂ within the RCA concrete with the conservation law of mass for the carbonatable substances. The proposed model adopted effective diffusion coefficient of CO₂, coefficient of carbonation reaction rate, amount of carbonatable substances and adhesive mortar of the RCA as major control parameters. Efficiency and applicability of the proposed model were validated by comparing with experimental data.

Abstract:The drilling parameters in the rotary drilling process were sampled and analyzed using online monitoring system. The theoretical expressions between the derived parameters and direct sampling parameters were constructed, and the model of formation work ratio considering multi-factor combinations was also proposed to realize the perfect integration of geological conditions and drilling parameters. With the case study of a construction field of the high voltage substation in Chongqing, the curves of different formations such as backfilled soil, silty clay sandstone and mudstone formations were described and compared with the geological survey, the comparison presented obvious difference of different formations. The above results indicated that rational work ratio thresholds were significant to identify the strata characteristics. And then, the work ratio threshold of different formations was optimized near the surveying piles based on the statistical analysis theory to prove the reliability of the threshold range of different formations according to the geological information. In addition, the threshold value were used to verify the formations far away from the surveying piles, the results deeply calibrated the proposed method and verified the rationality of the threshold values. Therefore, the proposed method to determine the threshold range based on formation work ratio model can be used to another different formations and strata identification.

Abstract:The method of that isolation layer of prototype structure simplified to model structure in shaking table test was systematically researched based on equivalent principle, similarity theory, and considered three-dimensional seismic effect. Aimed at isolated structure in different aspect ratio, complete equivalent and part of equivalent simplified method were proposed. Equivalent of isolation layer, model's parameters of isolation bearings, coordinate certainty, similarity theory and so on were included in the method. the method was verified with shaking table tests of isolated structure with different aspect ratio, and combined with finite element numerical simulation, Theoretical derivation and numerical simulation were certified that the simplified method possessed well accuracy. And within the error allowed, the same dynamic characteristics of acceleration, velocity, displacement of isolation layer before simplification could be obtained. Therefore, the method could be used in shaking table test of model design.

Abstract:At present, despite that the super soft soil foundation of the dredging silt is mainly strengthened by the vacuum-PVD consolidation method, the clogging is an important issue during the field application. With the vacuum preloading project of the Hengda Sea Flower Island in Hainan Province, a new type of anti-clogging vacuum preloading method for the super soft soil foundation is developed. It is the further improvement of the straight-line vacuum preloading method. The traditional PVD is replaced by the anti-clogging PVD, and the nonporous steel hose and tee sealing joint are also applied to update the traditional connections. Thereafter, the in-situ monitoring during vacuum and quality evaluation after construction is detailed introduced. The results verify the effectiveness and applicability of the preloading vacuum method' amendment. Combined with the existed laboratory model test, the principle of clogging in the vicinity of the PVD during vacuum preloading, and the mechanism of improved vacuum preloading are also discussed.

Abstract:Combined with water resistance of magnesium oxychloride cement concrete, the corrosion and protection for steel bar in magnesium oxychloride cement concrete were experimentally investigated, and the influencing factors included: the type of steel bar, thickness of the concrete protective layer and the corrosion duration. The two types of steel bar were bare steel bar and MAGNI coated steel bar. The two types of thickness of the concrete protective layer were 25 mm and 50 mm. The six types of the corrosion duration were 60 d, 120 d, 180 d, 240 d, 300 d and 360 d. 2/3 height of test block was prolonged soaked in water. By SEM and EDS, microstructure and chemical elements of steel bar with corrosion were analyzed to study corrosion mechanism. Result showed that by softening coefficient, the softening coefficient of magnesium oxychloride cement concrete was from 0.78 to 0.87, and the magnesium chloride cement concrete designed by this experiment could be used as a dry area, damp lighter area or secondary structure. By polarization curves and its electrochemical parameters, corrosion rate of bare steel bar was from 40 to 80 times as large as corrosion rate of MAGNI coated steel bar.

Abstract:The stress-strain relationship for expansive soil is associated with water content changing. Through the laboratory test of the relationship between the deformation, strength, expansion parameters of the expansive soil and the water content, a expansive soil elastic-plastic constitutive model based on Mohr Coulomb criterion which has engineering practical value is proposed according to the humidity stress field theory. In accordance with fundamental code-run-principle of FLAC3D software, the basic principle of the secondary development program and detailed analysis combined with the expansive soil elastic-plastic constitutive model are proposed. The correctness of the expansive soil constitutive model is verified through the demonstration calculation of an expansive soil slope, combined with the water content field calculated by Seepage software.

Abstract:The exterior joints of specially shaped columns with high-strength reinforcement, and with or without X-shaped reinforcement were tested under low cyclic loading. The damage characteristic, hysteretic curve, bearing capacity, displacement, ductility, stiffness degradation and energy dissipation capacity were compared. The results showed that for the exterior joints of specially shaped columns, the bearing capacity of the HRB500 joint was lower, but the hysteretic behavior, deformability, energy dissipation capacity were increased, the stiffness degradation was postponed. When X-shaped high-strength reinforcement added to the joints, the failure characteristics of the joint was improved, the stiffness degradation was postponed, the deformability, shear capability and energy dissipation capacity were increased, the seismic behavior of specially shaped column joints was improved significantly, and the seismic behavior of the HRB500 joint was improved more.

Abstract:Through spot pull-out destructive test, ultimate bearing capacity and slippage in the foundation slab of GFRP anti-floating anchors with different diameter were monitored. Compared with some kinds of steel anti-floating anchors in the actual engineering, their bearing performance and bond behavior were analyzed. The results showed that under the same strength and curing condition of the concrete, ultimate bearing capacity of GFRP anti-floating anchor was larger than steel anti-floating anchor with same diameter, the average bond strength between GFRP anti-floating anchor and foundation slab was higher than the steel anti-floating anchor, moreover the deformation of GFRP anti-floating anchor can meet the engineering requirements, all of those fully verify that GFRP material as an anti-floating anchor was advanced and reasonable. Based on the experimental results and theoretical analysis, the best anchoring area between GFRP anchor and foundation slab was determined, the computational formula was proposed.

Abstract:Most piles are set in layered soils. The initial foundation coefficient, a hyperbolic p-y curve containing a parameter, is derived to generally simulate the nonlinear soil around the pile. The soil around the tested pile is nonlinear, and both the tested and the calculated lateral displacement of the tested pile at the ground have a parabolic relation with the horizontal loads. The calculated lateral displacements of the tested pile at the ground fit the tested lateral displacements very well, and the hyperbolic p-y curve is proved good. The nonlinear soil will greatly increase both the maximum moment of the pile and the soil pressure. Thus it is suggested that the designed moment of the pile which is calculated by m-method, should magnified 1.05~1.25 times in order to consider the nonlinearity of the soil around the pile.

Abstract:Experiments on normal section flexural capacity with two groups of five ECC/high strength reinforced concrete composite beams were implemented to explore its flexural characters with different ECC depths. It was found that comparied with steel reinforced beams, composite beams gained more flexural capacity, and had the less deformation and crack width under the same load. Plane-section assumption was still applicable,strains between steel and ECC were also well accorded with, which showed that ECC could bring the high strength steel into full play, while it would happen brittle fracture when the ECC's depth increased to one half of the beam. On the basis above, combined with superposition principle, constitutive model of ECC was been simplified to neglect its stress hardening behavior, a new calculation method for the capacity of the composite beams was proposed. To verify the theory, results by the calculated and the experimented had been comparied.

Abstract:The dynamic compression strength of concrete which undergone cyclic loading and subjected to water pressure was carried out, and effect of water pressure and cyclic times on strength of concrete was analyzed. Strain rates of tests were 10^-5/s, 10^-4/s, 10^-3/s and 10^-2/s, and water pressure ranged from 0 to 10 MPa. The results showed that strength of saturated concrete under different water pressure increased with the increasing strain rate, and that also increased with the increasing water pressure. Under the same water pressure, the concrete strength increased more significantly when the strain rate was higher. After cyclic loading, strength of saturated concrete showed the phenomenon of the first increase and then decreased as the number of load cycles increased. The higher the strain rate, the greater number of load cycles with maximum concrete strength. The relationships between concrete strength and strain rate, water pressure were established, which was in good agreement with the experimental data. Furthermore, the pipe pore model was introduced, and the mechanism of pore water on the concrete strength was explained and based on the principle of mercury intrusion porosimetry and pore distribution.

Abstract:Three kinds of mixed solutions of sulfuric acid and nitric acid with the pH value of 1.5, 2.5 and 3.5 were prepared in the laboratory to simulate acid rain environment. The compression properties of brick masonry exposed to acid rain environment was studied. The brick samples, mortar samples and brick-columns were completely immersed in the simulated acid solutions. After being exposed to the solutions for a certain period, compression tests were performed on the three types of the samples. The results showed that with the increase of corrosion time the compressive strength of mortar samples increased firstly and then decreased, whilst the brick samples always decreased. And the lower the pH value of the solutions was, the more the compressive strength of mortar samples and brick samples decreased. With the increase of corrosion time, the ultimate bearing capacity and elastic modulus of brick-columns showed a trend of decrease, and the lower the pH value of the solutions was, the more obvious the trend was. With the increase of corrosion time, the initial stiffness of brick-columns decreased, ultimate failure displacement increased. With the pH value of the solutions declining, the deformation of brick-columns under ultimate load decreased but the brittleness increased. Based on the experimental results, regression formulas were put forward to describe the ascending part of the stress-strain curve and the remaining compressive strength of brick-columns exposed to acid rain environment.

Abstract:600 MPa steel bar was a new type of high-strength reinforcing bar. Seven T-shaped column specimens varying in stirrup ratios, axial compression ratios and steel strength were tested under low cyclic loading to investigate the feasibility of using this type of reinforcement in specially shaped column. Behaviors in bearing capacity, displacement, hysteretic behavior, skeleton characteristic, rigidity degradation and energy dissipation were investigated to analysis the seismic performance of columns. The results showed that 600 MPa RC T-shaped columns had favorable deformation capacity and bearing capacity. Improving stirrup ratios could effectively improve the seismic performance. With the increase of axial compression ratios, the bearing capacity of columns was bigger, but the deformation capacity deteriorated. With the improvement of the strength of steel, bearing capacity, deformation capacity significantly increased.

Abstract:Soil sedimentation and stress history have great impact on the determination of soil gravity stress and the final settlement of the foundation soil. Due to the accurate and convenient of coordinate in dealing with the linear problem over coordinate, thus it is often applied to calculate the influence of sedimentation and gravity stress of the normal consolidated soil and over-consolidated soil. This formula is to used to calculate the gravity stress value and final settlement value of deep soft clay which came from Kunming exhibition Center near Dianchi Lake, while the calculation result is used to make a comparison with historical data of stress value and settlement impact. The result showed that the sedimentation has great impact to the gravity and final settlement value of deep soft clay, furthermore, the thicker of the soil will bring the bigger of the overlying load consistently.